1. Field of the Invention:
This invention relates to an optical coupler of low insertion loss for use in the field of optical communication to switch from one light source to another without the slightest interruption.
2. Description of the Prior Art:
Semiconductor lasers available today as light sources for optical communications are deficient in reliability as compared with semiconductor elements. In the field of optical communications which requires high reliability, therefore, improvements in and concerning the reliability of such semiconductor lasers have been strongly in demand.
As a tentative measure to heighten the reliability of light sources for optical communications, adoption of a redundant construction in which two semiconductor lasers are alternatively put to use, one as an operating light source and the other as a stand by light source, has been conceived. To render this redundant construction practicable, there has been heretofore used a changeover switch constructed as illustrated in FIG. 1 for the purpose of enabling the operating light source to be switched to the standby light source.
This switch is formed of a movable prism 5. When the light signal emitted from a light source 1 and propagated through a fiber 3 is desired to be led to the main optical fiber 6, the movable prism 5 is moved to the upper position indicated by a dotted line. When the light signal emitted from a light source 2 and propagated through a fiber 4 is desired to be led to the main optical fiber 6, the movable prism 5 is moved to the lower position indicated by a continuous line. In this manner, the light signal from the light source 1 and that from the light source 2 are switched from one to the other by the switch which is formed of the movable prism 5.
This switch has features of low level in cross-talk. It nevertheless has a disadvantage that both reproducibility and reliability of the switching effected thereby are deficient because the prism is mechanically moved and, therefore, is susceptible of positional deviation.